Tilt sensors are employed in a wide variety of measuring instruments and are used in conjunction therewith in order to determine the orientation of the instrument or in order to confirm or reach a required position of a device. Such sensors are used particularly in the building industry and in the field of geodesy. In order to ensure that the coordinate determination of a target mark is carried out correctly and the position of a surveying device is in this case taken into account, besides the location of the device it is necessary to be able to record accurately its position relative to the Earth's gravitational field. Sensors of various designs are already known for the purpose of this tilt determination.
US 2002/0014590 A1 presents a tilt sensor having a CCD array as a detector. The sensors of the array are located on a wall of a container, which is in turn partially filled with a liquid. The tilt is determined by reading out the signals of the individual CCD sensors on the array and comparing them with one another.
The disadvantage of this sensor is that the measurement of the tilt can only be carried out in one direction. For the determination of an absolute tilt in two axes relative to a horizontal, a further measurement must be carried out after changing the location of the sensor or an additional second sensor of the same design must be used.
The laid-open specification DE 41 10 858 relates to a biaxial inclinometer, in which a geometrical figure is projected by means of a tilt-sensitive and beam-deflecting sensor onto a linear array. The sensor contains a liquid, the position of which relative to the device leads to influencing or deflection of the projection of the figure on the linear array.
Besides the disadvantages which are due to the complexity of their structure, inclinometers of this design are miniaturizable only to a limited extent owing to the required minimum length of the beam paths for two elementary beams.
EP 1 511 971 discloses an optical inclinometer in which radiation is emitted by a radiation source and is imaged onto a camera after passing through a holding element, which in particular contains a liquid. In this arrangement, the tilt of the inclinometer can be deduced from the position of the liquid horizontal relative to the inclinometer, or the camera. Recording the position of the medium by a camera furthermore permits evaluation of a multiplicity of features, in particular shape, extent and position of a boundary layer.
A disadvantage with this configuration is that the tilt can be carried out accurately only in one direction, referred to as longitudinal tilt, and the determination in a second direction, referred to as transverse tilt, is carried out with the aid of spreading of the image of the boundary layer. The variation of this image width can turn out to be very small for a minor variation of the transverse tilt, and can therefore be resolved and evaluated only with limited accuracy.